This study concentrated on two common membrane concentrate disposal options-direct surface water disposal and discharge into sewer. Mass balance evaluations were conducted to evaluate the feasibility of discharging membrane concentrate from hypothetical membrane water treatment facilities to several rivers. Feasibility was justified by compliance with the 30-day average TDS concentration imposed by surface water discharge permit requirements.; The study showed that the systems located at Pierre, Sioux Falls, Rapid City and Yankton would be amenable to both the disposal options whereas the systems at Bon Homme-Yankton, Huron and Vermillion would be amenable to the direct disposal option only. Neither of the disposal options can be adopted for the systems at Watertown and Aberdeen. Additional study would be necessary to assess the sewer disposal option at Brookings.; The set up of new membrane plants will eventually remove all the home based water softeners from the water distribution system. As a result, there will be less inflow of Na+ and Cl- into the wastewater treatment plants and eventually the effluent water will contain a lower TDS concentration.
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